Tissue Test for Excess Nitrogen during Corn Production
Seeming conflict between the need to use N fertilizers and the need to protect groundwater quality requires better tools for distinguishing between fertilizer applications that are essential and those that are excessive. Studies were conducted to evaluate NO-3 concentration in corn (Zea mays L.) stalks at physiological maturity as the basis for a tissue test to characterize degree of N excess during coin production. Samples of the lower portion of corn stalks were collected from plots in N-rate experiments at 18 site-years in Iowa. Observed relationships between grain yields and stalk NO-3 concentrations indicated sharp breaks between NO-3 concentrations that were not adequate and those that were adequate for obtaining maximum or near-maximum yields. When yields were near maximum, stalk NO-3 concentrations increased linearly with amounts of N fertilizer applied. Stalk samples collected at various times after black layering showed that NO-3 concentrations remained constant for at least 2 wk. These observations suggest that stalk NO-3 concentration offers great potential as the basis for a tissue test to characterize degree of N excess during corn production.
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